Anodizing apparatus

ABSTRACT

An anodizing apparatus includes: a power supplying drum for supporting a strip of an anodizable metal or a composite conductive foil having an anodizable metal on one surface thereof in close contact, at least a portion of the power supplying drum supporting the strip being conductive; opposing electrodes facing the power supplying drum; an electrolysis tank filled with an electrolytic solution in which a portion of the power supplying drum that supports the strip and the opposing electrodes are immersed; non conductive protective members that overlap the transverse ends of the strip on the power supplying drum and portions of the power supplying drum that the strip is not in contact with to protect the overlapped portions from the electrolytic solution; and a drive section that causes the strip and the protective members to move together within the electrolytic solution, synchronized with the rotating speed of the power supply drum.

TECHNICAL FIELD

The present invention is related to an anodizing apparatus suited for producing substrates for semiconductor elements and electrodes for electrolytic capacitors, which are used in semiconductor devices such as solar batteries, thin film transistor circuits and displays (image display devices).

BACKGROUND ART

There are greater possibilities for application of thin film solar batteries that employ metal substrates compared to those that employ glass substrates from the viewpoints of the light weight and the flexibility thereof. Further, there are expectations for higher efficiency of solar batteries because metal substrates can endure high temperature processes, therefore improving the photoelectric conversion properties thereof.

The module efficiency of a solar battery module is improved by connecting solar battery cells in series on a single substrate and integrating the solar battery cells. At this time, it is necessary to form an insulating layer on the metal substrate of the solar battery module and to provide a semiconductor circuit layer for performing photoelectric conversion on the insulating layer. For example, in the case that a steel series material such as stainless steel is employed as a substrate, it is necessary to form an insulating layer by coating the substrate with an Si oxide or an aluminum oxide by a vapor phase method such as CVD or a liquid phase method such as the sol gel method. However, pinholes and cracks are likely to be generated in the insulating layers if they are formed by these methods, and there is a practical problem in stably producing thin film insulating layers having large areas (Patent Document 1).

Meanwhile, in the case that aluminum is employed as a substrate, an insulating coating layer having favorable close contact properties without pinholes can be obtained by forming an anodized film of AAO (Patent Document 2). However, it is known that cracks are generated in AAO on aluminum if the AAO is heated to 120° C. or greater (Non Patent Document 1), resulting in problems that the insulating properties deteriorate, particularly that leakage current increases. In addition, aluminum softens at approximately 200° C., and therefore the integrity of aluminum which has reached this temperature or greater is extremely small. Permanent deformation (plastic deformation) such as creep deformation and buckling deformation becomes likely to occur in such aluminum, and severe restrictions regarding handling are necessary when producing semiconductor devices using such aluminum. This results in application of aluminum substrates to outdoor solar batteries becoming difficult.

In order to solve the aforementioned problem, a method for forming AAO as an insulating layer on a substrate formed by a so called aluminum cladding material, and then forming a light absorbing composite semiconductor layer or an electrode layer on the layer of AAO has been proposed. In this method, it is possible to design the layers such that the difference between the coefficients of thermal expansion of the metal substrate and the composite semiconductor layer is small. Therefore, problems such as cracking of the insulating layer and peeling of the composite semiconductor layer do not occur even during a step of forming the composite semiconductor layer, which is executed at a high temperature of 500° C. or greater. In addition, the metal base material which is combined with the aluminum has higher specific strength and higher high temperature health compared to aluminum, and therefore handling during production is facilitated.

It is not only necessary for the insulating function of AAO to not fail at high voltages when AAO is employed as an insulating layer of a battery module, but also necessary for the amount of leakage current to be small when voltage is applied. That is, it is necessary for the AAO insulating layer to have a high volume resistance. If the amount of leakage current is great, the generated current will become leakage current among individual batteries, and the electricity generating efficiency of the module will deteriorate. Accordingly, it is necessary for the thickness of AAO to be 1 μm or greater, and preferably 5 μm or greater, in order to guarantee the aforementioned performance.

A common apparatus for continuously anodizing aluminum strips is of a configuration in which a power supplying roll or a power supplying tank is placed before an electrolysis tank, to supply electric current to the aluminum. The electric current also flows through the aluminum from the power supplying portion to the electrolysis tank. Anodization is electrolytic oxidation (a three electron reaction in the case of aluminum), and the thickness of AAO is proportionate to the amount of electric current that flows through the aluminum. Accordingly, it is necessary to supply electrical current proportionate to the line speed (the speed at which the aluminum strip is moved). At this time, the same proportionate electric current flows through the aluminum from the power supply portion to the electrolysis tank. Therefore, voltage drop becomes greater and power loss is generated the thicker the AAO is and the greater the line speed is. Further, there is a possibility that meltdown will occur in the aluminum between the power supply portion and the electrolysis tank due to IR heat generation, and there are upper limits to the thickness of AAO and the line speed. Heat generation and meltdown limit current are determined by the resistance of the aluminum strip per unit cross sectional area. Therefore, the upper limits of the possible thickness of AAO and the line speed will become smaller as the aluminum foil becomes thinner.

Meanwhile, there is demand to form a thick AAO layer on only one surface of a thin strip of aluminum foil. An example of such applications is the aforementioned metal substrate having an insulating layer. In this case, it is possible to attach a masking film to one surface and to produce the AAO layer using the aforementioned apparatus. However, there are upper limits to the thickness of AAO and line speed. In addition, AAO is a subtractive coating film, which is different from an additive coating film such as those formed by plating. Therefore, a coating film will be formed easily in the case that electrolytic solution enters from the edges of the masking film. Accordingly, it is necessary to select a masking film having highly adhesive properties. Further, in the case of a strip of metal foil in which different types of metals are joined, such as a cladding material, it is necessary for a masking film to be adhesively attached to the side edge surfaces at which the different types of metals are exposed, in order to render them electrochemically inactive to prevent side reactions due to local battery operations.

Various apparatuses for forming AAO films on only one of the surfaces of aluminum strips have been proposed. A representative example is that in which a supporting drum having a circular cross section is placed in an anodizing tank, placing aluminum foil in close contact with the drum, and anodizing only one of the surfaces of the aluminum foil (Patent Document 3). In addition, a method in which a supporting drum has conductive properties and is caused to supply power has also been proposed (Patent Document 4). In the latter case, power can be supplied directly from the back surface of aluminum foil, and therefore the aforementioned voltage drops and heat generation can be suppressed to a level that can be ignored.

However, seepage of electrolytic solution between the support drums and the aluminum foil occurs easily in these techniques. AAO is formed on the side of the aluminum foil toward the anodizing tank, causing excess voltage at this side to become great. Therefore, if electrolytic solution seeps into the supporting drum, direct current between the supporting drum and opposing electrodes will become great, resulting in current loss with respect to the AAO coating film forming current at the side toward the anodizing tank. In addition, this current loss will have an electrochemical effect on the surface of the power supplying drum with which the aluminum foil is in close contact. Accordingly, there is a possibility that an anodized film will be formed on the aluminum on the side in contact with the power supply drum, that the surface of the power supplying drum will become anodized or undergo anodic dissolution if the power supplying drum is formed by metal, resulting in contact resistance increasing at the close contact surface and local defects such as sparks being generated.

In order to solve the aforementioned problem, Patent Document 4 proposes an apparatus in which the material of the power supplying drum is a so called valve metal such as tantalum and niobium. However, an anodized coating film will grow on the surface of the valve metal accompanying electrolytic operations in this apparatus. Accordingly, contact resistance will gradually increase, and it is necessary for the power supply drum to be replaced often. However, such materials are expensive, and frequent replacement is not practical. Meanwhile, Patent Document 5 proposes a technique for preventing electrochemical effects from occurring at a close contact surface between aluminum foil and a support roller, by supplying water to the close contact surface. In addition, Patent Document 6 discloses a configuration in which the two edges of aluminum foil are covered by non conductive compression band under tension, to prevent electrolytic solution from flowing into a contact surface.

Prior Art Documents Patent Documents

-   [Patent Document 1] -   Japanese Unexamined Patent Publication No. 2001-339081 -   [Patent Document 2] -   Japanese Unexamined Patent Publication No. 2000-049372 -   [Patent Document 3] -   Japanese Unexamined Patent Publication No. 4(1992)-371892 -   [Patent Document 4] -   Japanese Unexamined Patent Publication No. 60(1985)-211093 -   [Patent Document 5] -   Japanese Unexamined Patent Publication No. 6(1994)-108289 -   [Patent Document 6] -   Japanese Unexamined Patent Publication No. 46(1971)-039441

Non Patent Documents

-   [Non Patent Document 1] -   M. Kayashima and M. Mushiro, “Heat-induced cracking of anodic oxide     films on aluminum—An in suit measurement of the cracking     temperature—”, Tokyo Metropolitan Industrial Technology Research     Institute Research Report, Vol. 3, pp. 21-24, 2000

However, the apparatus of Patent Document 5 is not only complex, but the electrolytic solution will be diluted by the water on the close contact surface, and therefore it is necessary to constantly maintain the concentration of the electrolytic solution. In addition, if the thin layer of water on the contact surface generates gas due to electrolysis, the thin film will become a gaseous film, increasing the contact resistance. As a result, there is a possibility that employing this apparatus will cause sparks to be generated. Meanwhile, in the method for covering the edges of the aluminum foil with the bands under tension disclosed in Patent Document 6, the bands are constantly in sliding contact with the power supplying drum and the aluminum foil. Therefore, the positions of the bands are likely to shift away from the edges of the aluminum foil, and it is difficult for continuous anodizing operations to be performed. In addition, wrinkles will be generated by the tension being applied under pressure in the case that the aluminum foil is thin, and there is a possibility that electrolytic solution will flow into the space between the aluminum foil and the drum through the wrinkled portions.

As described above, none of the methods described above can completely prevent anodized coating film formation on the side of the close contact surface. Therefore, the problem that contact resistance will be unstable cannot be solved.

The present invention has been developed in view of the foregoing circumstances. It is an object of the present invention to provide an anodizing apparatus capable of forming anodized films on a single surface of a thin metal substrate or a metal substrate having high resistance at high speed.

DISCLOSURE OF THE INVENTION

The anodizing apparatus of the present invention is characterized by comprising:

a power supplying drum for supporting a strip of an anodizable metal or a strip of a composite conductive metal foil having an anodizable metal on at least one surface thereof in close contact, at least a portion of the power supplying drum which is in close contact with the strip being constituted by a conductive material;

opposing electrodes provided to face the power supplying drum;

an electrolysis tank filled with an electrolytic solution in which a portion of the power supplying drum that supports the strip in close contact and the opposing electrodes are immersed;

protective members formed by a non conductive material that overlaps the transverse ends of the strip supported by the power supplying drum in close contact and portions of the power supplying drum with which the strip is not in close contact to protect the ends and the portions of the power supplying drum from the electrolytic solution; and

a drive section that causes the strip in close contact with the power supplying drum and the protective members to move together within the electrolytic solution, synchronized with the rotating speed of the power supply drum.

It is preferable for a recess that the strip contacts and moves within to be provided in the power supplying drum.

The anodizing apparatus may further comprise: guide rollers for pressing the protective member onto the power supplying drum.

It is preferable for a plurality of apertures to be provided in the opposing electrodes.

It is preferable for the distance between the power supplying drum and the opposing electrodes at the portion of the strip supported by the power supplying drum that enters the electrolytic solution and/or the portion of the strip that exits the electrolytic solution to be greater than the distance between the power supplying drum and the opposing electrodes at a central portion of the strip immersed in the electrolytic solution.

It is preferable for the protective member to be non conductive rubber or a metal foil covered by nonconductive rubber.

It is preferable for the conductive material of the power supplying drum to be conductive plastic or conductive rubber.

It is preferable for the electrical potential of the opposing electrodes to be a negative polarity with respect to ground.

It is preferable for the electric potential of the strip to be the same as ground, and the output of an electrolytic power source to be insulative with respect to ground.

It is preferable for the anodizing apparatus to further comprise: a monitoring section for monitoring the voltage of the power supplying drum with respect to the electrical potential of ground.

A continuous anodizing apparatus of the present invention is characterized by comprising:

a plurality of the anodizing apparatuses of the present invention, arranged in series.

The anodizing apparatus of the present invention comprises: a power supplying drum for supporting a strip of an anodizable metal or a strip of a composite conductive metal foil having an anodizable metal on at least one surface thereof in close contact, at least a portion of the power supplying drum which is in close contact with the strip being constituted by a conductive material; opposing electrodes provided to face the power supplying drum; an electrolysis tank filled with an electrolytic solution in which a portion of the power supplying drum that supports the strip in close contact and the opposing electrodes are immersed; protective members formed by a non conductive material that overlaps the transverse ends of the strip supported by the power supplying drum in close contact and portions of the power supplying drum with which the strip is not in close contact to protect the ends and the portions of the power supplying drum from the electrolytic solution; and a drive section that causes the strip in close contact with the power supplying drum and the protective members to move together within the electrolytic solution, synchronized with the rotating speed of the power supply drum. Therefore, it is possible to completely prevent anodized coating film formation on the side of the strip in close contact with the power supplying drum, and an anodized coating film can be formed on a single surface of the strip with stable contact resistance.

In addition, the strip is supported in close contact by the power supplying drum, enabling direct power supply from the back surface of the strip. Therefore, voltage drops and heat generation can be suppressed to a level that can be ignored, enabling line speed to be increased. For this reason, an anodized coating film can be formed at high speed even if the resistance of the strip per length at a unit width is high.

Further, a recess that the strip contacts and moves within may be provided in the power supplying drum, or guide rollers for pressing the protective member on to the power supplying drum may be provided. In these cases, the waterproof properties of the portion at which the protective member overlaps the ends in the transverse direction of the strip and the portions of the power supply drum at which the strip is not in close contact with the power supply drum are improved. Therefore, an anodized coating film can be formed on a single surface of the strip with more stable contact resistance.

In addition, the continuous anodizing apparatus of the present invention is that in which a plurality of the anodizing apparatuses of the present invention are arranged in series. Therefore, production at a line speed·N (N is the number of anodizing apparatuses) is enabled while maintaining the surface current density at a maximum value at which anodization failures do not occur in the power supplying drum of each anodizing apparatus. As a result an AAO film having a thickness of 5 μm or greater can be formed at high speed on a thin strip of aluminum having high resistance or on a strip of a composite conductive metal foil having aluminum on at least one surface thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view that illustrates an. anodizing apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic sectional view of the anodizing apparatus of FIG. 1.

FIG. 3 is a schematic front view of a power supplying drum having a recess with which a strip contacts and is moved within.

FIG. 4 is a schematic diagram that illustrates the relationships among the width and diameter of a power supplying drum, a strip, and protective members.

FIG. 5 is a schematic sectional view that illustrates an anodizing apparatus equipped with guide rollers according to another embodiment of the present invention.

FIG. 6 is a schematic front view that illustrates a power supply drum provided with the guide rollers of FIG. 5.

FIG. 7 is a schematic perspective view that illustrates an anodizing apparatus in which the electrical potential of opposing electrodes is set to a negative polarity with respect to ground.

FIG. 8 is a schematic diagram that illustrates a continuous anodizing apparatus in which a plurality of the anodizing apparatuses of the present invention are arranged in series.

FIG. 9 is a graph that illustrates the relationship between running speed and AAO film production speed.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, anodizing apparatuses of the present invention will be described in detail with reference to the attached drawings. FIG. 1 is a schematic perspective view that illustrates an anodizing apparatus 10 according to an embodiment of the present invention. FIG. 2 is a schematic sectional view of the anodizing apparatus 10 of FIG. 1. As illustrated in FIG. 1 and FIG. 2, the anodizing apparatus 10 of the present invention includes: a power supplying drum 2 for supporting a strip 1 of an anodizable metal or a strip 1 of a composite conductive metal foil having an anodizable metal on at least one surface thereof (hereinafter, also simply referred to as “strip 1”) in close contact, at least a portion 2 a of the power supplying drum which is in close contact with the strip 1 being constituted by a conductive material; opposing electrodes 3 provided to face the power supplying drum 2 (the opposing electrodes 3 is omitted from FIG. 1 in order to facilitate visual understanding of the other components); an electrolysis tank 5 filled with an electrolytic solution 4 in which a portion of the power supplying drum 2 that supports the strip 1 in close contact and the opposing electrodes 3 are immersed; and protective members 6 formed by a non conductive material that overlaps the transverse ends of the strip 1 supported by the power supplying drum 2 in close contact and portions 2 b of the power supplying drum 2 with which the strip 1 is not in close contact to protect the ends and the portions 2 b of the power supplying drum 2 from the electrolytic solution 4.

Further, a supply roll 21 for supplying the strip 1 is provided upstream from the power supplying drum 2, and a take up roll 22 for taking up the strip 1 sent out from the power supplying drum 2, onto one surface of which an anodizing process has been executed. In addition, supply rolls 23 for supplying the protective members 6 is provided between the supply roll 21 and the power supplying drum 2, and take up rolls 24 for taking up the protective members 6 are provided between the power supplying drum 2 and the take up roll 22. The supply rolls 23 and the take up rolls 24 are provided at both sides of the strip 1 such that the protective members 6 overlap the strip 1 and the portions 2 b with which the strip 1 is not in close contact. Drive sections (not shown) are provided in each of the take up rolls 22 and 24, and the drive sections are configured to cause the strip 1 in close contact with the power supplying drum 2 and the protective members 6 to move together, synchronized with the rotating speed of the power supplying drum 2.

Note that here, a case in which the drive sections provided in the take up rolls 22 and 24 drive each of the take up rolls 22 and 24 to take up the strip 1 after the anodizing process has been executed and the protective members 6. Alternatively, the take up rolls 22 and 24 may be configured to be freely rotatable and function merely to send out the strip 1 and the protective members 6, and take up rolls controlled by separate drive sections may be provided further downstream therefrom. In the case that this configuration is adopted, a water cleansing tank for cleansing the anodized strip and a drying tank for during the strip after being cleansed with water may be provided between the take up roll 22 and the other take up roll driven by the separate drive section.

The power supplying drum 2 itself is configured to be freely rotatable. The power supplying drum 2 conveys the strip 1 in a state in which only a single surface thereof is immersed in the electrolytic solution 4 by the drive sections described above driving the take up rolls 22 and 24. Alternatively, a drive source may be provided in the power supplying drum 2 and the power supplying drum 2 may be driven to rotate on its own.

The diameter of the power supplying drum 2 depends on the production scale and the anodized film formation speed, but is commonly selected as appropriate from within a range from 50 cm to 500 cm. The portion 2 a of the power supplying drum 2 that the strip 1 is in close contact with is constituted by a conductive material. The width of the conductive material is not necessarily the same as the width of the strip 1, and may be that which can accommodate zigzagging of the strip 1. The width of the conductive material is preferably within a range from 50% to 100% of the width of the strip 1, and more preferably within a range from 70% to 90% of the width of the strip 1.

In anodization, the planar current density is generally 500 mA/cm² or less. Therefore, it is not necessary for the conductive portion of the power supplying drum to have conductivity greater than 500 mA/m². In addition, in the case that the conductive material of the power supplying drum is a metal, there is a possibility that contact resistance will change over time due to an oxidized film being formed by mist of the electrolytic solution. Therefore, it is preferable for the conductive portion of the power supplying drum to be conductive plastic or conductive rubber. The surfaces of these materials are soft, and therefore use of these materials is also effective in preventing damage to the surface of the strip which is not anodized. Materials for general use, into which carbon is mixed to impart conductivity, may be utilized as the conductive plastic or the conductive rubber. The thickness of the conductive plastic or the conductive rubber will differ depending on desired strength and conductive properties. However, it is preferable for the thickness of the conductive plastic or the conductive rubber to be within a range from 0.1 mm to 10 mm. The portions 2 b of the power supplying drum 2 with which the strip 1 does not closely contact are constituted by a non conductive material. Non conductive plastic, non conductive rubber, etc., are preferred as the non conductive material.

It is preferable for the protective members to be formed by non conductive rubber, or to be metal foils covered by non conductive rubber. A material having adhesive properties may be coated on the surfaces of the protective members toward the sides that closely contact the strip 1.

Although this depends on the diameter of the power supplying drum, it is preferable for tension to be applied to the protective members that move together therewith in order to secure waterproof properties. In the case that the diameter of the power supplying drum is great, non conductive rubber belts having steel cores may be favorably utilized as the protective members.

The strip is formed by an anodizable metal or a composite conductive metal foil having an anodizable metal on at least one surface thereof. Anodizable metals include: aluminum, Nb, Ta, and Ti. The metal may be an alloy. For example, aluminum alloys may be utilized in addition to pure aluminum. Aluminum alloys having purities of 90% or greater can be favorably employed. In the case that the anodized coating film is to be utilized as an insulating layer, it is preferable for the strip to not include metal Si particles as precipitates.

Examples of metals to be combined with the anodizable metal to form the composite conductive metal foil include: iron, carbon steel, stainless steel, and Ti. The thickness of the strip is generally within a range from 0.02 mm to 0.5 mm. An anodized coating film can be formed at high speed even on strips having high resistance per length at a unit width, because the strip is supported in close contact with the power supplying drum, and power can be directly supplied from the back surface of the strip.

Examples of the electrolytic solution include: acids, such as sulfuric acid, phosphoric acid, chromic acid, oxalic acid, tartaric acid, malonic acid, sulfamic acid, benzenesulfonic acid, and amidosulfonic acid; solutions of salts of the acids; and mixtures thereof. An optimal electrolytic solution may be selected in order to obtain a desired quality. The concentration and the temperature of the electrolytic solution may also be selected as appropriate.

The anodizing apparatus of the present invention moves the strip 1 in close contact with the power supplying drum 2 and the protective members 6 that overlap the ends of the strip 1 in the transverse direction thereof and the portions 2 b at which the strip 1 is not in close contact together within the electrolytic solution, synchronized with the rotating speed of the power supply drum 2. Therefore, seepage of the electrolytic solution 4 can be prevented without employing masking films, which had been conventionally necessary when forming anodized coating films on single surfaces of strips. In addition, because the edge portions of the strip 1 in the transverse direction thereof are completely protected by the protective members 6. Therefore, side reactions due to local battery effects will not occur even in the case that anodization is performed on a strip in which different types of metals are joined such as cladding material. Because it is possible to completely prevent anodized coating film formation on the side of the strip in close contact with the power supplying drum, an anodized coating film can be formed on a single surface of the strip with stable contact resistance at high speed.

In the anodizing apparatus of the present invention, the diameter of the portion of the power supply drum 2 along which the strip 1 and the protective members 6 move may be made smaller to suppress zigzagging of the protective members 6 that overlap the strip 1, in order to further improve the waterproof properties of the protective members 6 that overlap the strip 1. A description of such a configuration will be described with reference to FIG. 3 and FIG. 4. FIG. 3 is a schematic front view of a power supplying drum having a recess with which a strip and protective members contact and are moved within. FIG. 4 is a schematic diagram that illustrates the relationships among the width and diameter of a power supplying drum, a strip, and protective members. Note that in FIG. 3 and FIG. 4, elements which are equivalent to those illustrated in FIG. 1 and FIG. 2 are denoted with the same reference numerals, and detailed descriptions thereof will be omitted insofar as they are not particularly necessary (the same applies to the other drawings as well).

As illustrated in FIG. 3 and FIG. 4, a recess (cutout portion) that the strip 1 contacts and moves within and recesses that the protective members 6 contact and move within are provided in the power supplying drum 2. In FIG. 4, W₃ and D₃ respectively denote the width and diameter of the power supply drum 2, W₂ and D₂ respectively denote the width and diameter of the outer sides of the portion of the power supplying drum 2 that the protective members 6 contact, and W₁ and D₁ respectively denote the width of the strip 1 and the diameter of the portion of the power supplying drum 2 that contacts the strip 1. Zigzagging of the protective members 6 that overlap the strip 1 is suppressed by the recesses provided in the power supplying drum by setting the relationship among the diameters of the drum to be D₃>D₂>D₁. The strip 1 is overlapped by the protective members 6 with high waterproof properties by setting the relationship among the above widths to be W₃>W₂>W₁. Thereby, entry of electrolytic solution to the back surface of the strip 1 can be more effectively prevented. Note that here, a case was described in which a recess that the strip 1 contacts and moves within and recesses that the protective members 6 contact and move within are provided in the power supplying drum 2. Alternatively, only a recess that the strip 1 contacts and moves within may be provided in the power supplying drum 2.

The anodizing apparatus of the present invention may be provided with guide rollers that press the protective members 6 against the power supplying drum 2. A description of such a configuration will be described with reference to FIG. 5 and FIG. 6. FIG. 5 is a schematic sectional view that illustrates an anodizing apparatus equipped with guide rollers according to another embodiment of the present invention. FIG. 6 is a schematic front view that illustrates a power supply drum provided with the guide rollers of FIG. 5. As illustrated in FIG. 5 and FIG. 6, the anodizing apparatus is provided with four guide rollers 7 for pressing the protective members 6 that overlap the ends of the strip 1 in the transverse direction thereof and the portions 2 b that the strip 1 is not in close contact with. Note that the surfaces of the guide rollers are processed to be insulative. The strip 1 can be overlapped by the protective members 6 with improved waterproof properties by providing the guide rollers 7, and entry of the electrolytic solution onto the back surface of the strip 1 (the surface in close contact with the power supplying drum) can be prevented.

Note that here, a case is illustrated in which the guide rollers 7 are provided only at portions of the power supplying drum 2 which are immersed in the electrolytic solution 4. Alternatively, the guide rollers 7 may also be provided at portions of the power supplying drum 2 which are not immersed in the electrolytic solution 4. For example, zigzagging of the protective members 6 can be prevented even if the guide rollers 7 are provided only at portions of the power supplying drum 2 which are not immersed in the electrolytic solution 4 (positions between the supply rolls 23 and the electrolytic solution 4 and positions between the take up rolls 24 and the electrolytic solution 4). Therefore, it is possible for the protective members 6 to overlap the strip 1 and the portions 2 b with which the strip 1 is not in close contact with improved waterproof properties.

In anodization, a great amount of hydrogen gas is generated from the opposing electrodes during reactions and floats upward to reach the surface of the strip to be anodized. Anodization defects will be generated if a gaseous film is formed on the surface to be anodized, and therefore it is necessary to agitate the electrolytic solution within the electrolysis tank. It is preferable for a plurality of apertures to be provided in the opposing electrodes to improve the efficiency of agitation. The shapes of the apertures will differ depending on the manner of agitation (a stirrer may be used to perform agitation in a small apparatus, while current may be generated in the electrolytic solution in a large apparatus). However, the shapes of the apertures may be selected as appropriate from among circles, polygons, slits, or mesh. The sizes of the aperture will differ depending on the distance between the power supplying drum and the opposing electrodes. However, it is not preferable for the aperture size to be excessively large from the viewpoint of applying a uniform electric field onto the surface to be anodized. For example, in the case that the distance between the power supplying drum and the opposing electrodes is 10 cm, it is preferable for the diameters of circular apertures to be 2 cm or less.

Note that electrodes for general use formed by carbon, aluminum, etc., may be utilized as the opposing electrodes.

Direct current is commonly employed as the power source waveform during anodization. However, an optimal waveform such as an alternate current waveform in which direct current waveforms overlap each other may be selected in order to obtain a desired quality. The current density during anodization may be selected freely. For example, the current density may be a constant value during the entire anodization process, or increased during the anodization process. The electrolysis method employed during anodization may be a constant current method or a constant voltage method.

Anodization forms anodized coating film by assuming an electrical potential which is of a positive polarity with respect to the opposing electrodes. It is preferable for voltage to be applied to the opposing electrodes such that the electrical potential thereof is of a negative polarity with respect to ground. By adopting this configuration, the electrical potential of the strip can be set to be close to the electrical potential of ground, and it becomes possible to set the electrical potential of the entire installation that handles the strip on a roll to roll basis to ground. In the opposite case, it becomes necessary to impart electrical potential with respect to ground to the entire installation. This is not only dangerous, but there is also a possibility that abnormal discharge such as sparks will occur between the strip and the installation, resulting in defects in the finished product.

It is particularly preferable for the electric potential of the strip to be the same as ground, and for both a positive polarity output and a negative polarity of an electrolytic power source to be insulative with respect to ground. By adopting this configuration, abnormal discharge between the strip and the installation can be completely prevented at roll to roll portions other than the electrolysis tank. FIG. 7 schematically illustrates such a configuration. It is possible to set the electrical potential of the strip 1 to ground by providing at least one conductive roll 30 at a roll to roll portion other than the electrolysis tank 5, and to electrically connect the roll 30 to ground.

Further, it is preferable to monitor the voltage of the power supplying drum with respect to ground electrical potential in the case that the electrolysis method (the method by which electric current is caused to flow between the power supplying drum and the opposing electrodes) is the constant current method or the constant voltage method. By adopting this configuration, it becomes possible to monitor the cause of changes in the quality of the anodized coating film in the longitudinal direction of the strip, such as leakage current being generated due to temporary deterioration of the waterproof properties of the protective members and changes in to contact resistance between the strip and the power supplying drum.

It is preferable for the opposing electrodes 3 to be provided at substantially equidistant intervals across the entirety of the surfaces thereof that face the strip 1 in close contact with the power supplying drum 2 immersed in the electrolytic solution. It is preferable for the shapes of the opposing electrodes 3 to be curved plates which are concentric with the power supplying drum 2. However, if the opposing electrodes 3 are completely equidistant with from the power supplying drum 2 within the electrolytic solution, electrical current concentration caused by electrical field concentration will be generated at the portion of the strip to be anodized that enters the electrolytic solution 4 and at the portion that exits the electrolytic solution 4, which may result in anodization failures. Therefore, it is preferable for the effective electric field to be small. Utilizing the resistance of electrolytic solution is an simple method for decreasing the effective electric field, and the opposing electrodes may be arranged such that the distance between the opposing electrodes and the power supplying drum is greater at the portion of the strip that enters the electrolytic solution and/or the portion of the strip that exits the electrolytic solution. Alternatively, the opposing electrodes may be arranged such that no opposing electrode is provided at the portion of the strip that enters the electrolytic solution and/or the portion of the strip that exits the electrolytic solution.

FIG. 2 illustrates an arrangement of opposing electrodes in which the distance between the power supplying drum 2 and the opposing electrodes 3 is greater at the portion of the strip that enters the electrolytic solution and at the portion of the strip that exits the electrolytic solution. That is, a distance P₁ between the power supplying drum 2 and the opposing electrodes 3 at the portion at which the strip 1 supported by the power supplying drum 2 enters the electrolytic solution 4 and a distance P₂ between the power supplying drum 2 and the opposing electrodes 3 at the portion at which the strip 1 exits the electrolytic solution 4 are set to be grater than a distance P₃ between the power supplying drum 2 and the opposing electrodes 3 at the central portion of the strip 1 immersed in the electrolytic solution 4. Here, the distances P₁ through P₃ are the shortest distances between the power supplying drum and the opposing electrodes. By arranging the opposing electrodes in this manner, the effective electric field can be decreased, and the occurrence of anodization defects can be suppressed. Note that an arrangement in which the opposing electrodes are not provided at the portions at which the strip enters and exits the electrolytic solution is illustrated in FIG. 5.

Strips generally undergo a cleansing process as a preliminary step to an anodization process. The cleansing process removes contaminants from the surface of aluminum. For the same of convenience, a known method such as immersing the strip in an alkali solution that functions to dissolve natural oxidized coating films and remove contaminants is employed. A surface roughening process may also be administered as necessary. The surface roughening process provides protrusions and recesses on the surface of the anodized coating film, to improve close contact properties of the anodized coating film with another layer to be formed thereon. Known methods, such as the mechanical surface roughening process, the chemical surface roughening method, the electrochemical surface roughening method, and combinations thereof may be employed as the surface roughening process. The anodizing apparatus of the present invention may be provided with a preliminary processing tank for administering such preliminary processing steps and a water cleansing tank for cleansing and removing processing liquids upstream of the supply roll 21.

Meanwhile, the strip on which an AAO film is formed after the anodizing process generally undergo a drying process after passing through a water cleansing tank that cleanses and removes the electrolytic solution.

Next, the operation of the anodizing apparatus of the present invention will be described with reference to FIG. 1 and FIG. 2. First, the strip 1 which is wound about the supply roll 21 is rolled out and supported by the power supplying drum in close contact, then wound about the take up roll 22. Similarly, the protective members 6 which are wound about the supply rolls 23 are rolled out and wound about the take up rolls 24. At this time, the protective members 6 are caused to overlap the transverse ends of the strip 1 supported by the power supplying drum 2 in close contact and portions 2 b of the power supplying drum 2 with which the strip 1 is not in close contact in order to prevent entry of the electrolytic solution into the back surface of the strip 1. After this state is achieved, a portion of the power supplying drum 2, for example, down to the center of the drum, is immersed in the electrolytic solution 4 in the electrolysis tank 5. Then, the drive sections are driven to cause the strip 1 in close contact with the power supply drum 2 and the protective members 6 to move together within the electrolytic solution 4 synchronized with the rotating speed of the power supply drum 2. When the power source of the anodizing apparatus 1 is turned on, current flows between the power supplying drum 2 and the opposing electrodes 3, and an anodized film is formed on the surface of the strip 1 which is not in close contact with the power supplying drum 2.

A continuous anodizing apparatus illustrated in FIG. 8 is of a configuration in which three anodizing apparatuses 10 a, 10 b, and 10 c are arranged in series. The continuous anodizing apparatus is configured such that the strip 1 is supplied from the supply roll 21, passes through the anodizing apparatuses 10 a, 10 b, and 10 c, then is taken up via the take up roll 22 via transmitting rolls 25 a, 26 a, 25 b, 26 b, 25 c, and 26 c. The protective members 6 are supplied from the supply rolls 23, pass through the anodizing apparatuses 10 a, 10 b, and 10 c, then are taken up via the take up rolls 24 via transmitting rolls 27 a, 28 a, 27 b, 28 b, 27 c, and 28 c.

A preliminary processing tank 11 for administering preliminary processes onto the strip 1 is provided between the supply roll 21 and the transmitting roll 25 a. A water cleansing tank 12 for cleansing the anodized strip with water and a drying tank 13 for drying the strip 1 after it is cleansed are provided between the transmitting roll 26 c and the take up roll 22. Note that the continuous anodizing apparatus illustrated in FIG. 8 is that in which the protective members 6 are used jointly by the anodizing apparatuses 10 a, 10 b, and 10 c which are arranged in series. Alternatively, each of the anodizing apparatuses 10 a, 10 b, and 10 c may be provided with separate supply rolls 23 and take up rolls 24.

Although anodization of aluminum depends on the electrolytic solution and electrolysis conditions, the coulombic efficiency of electrolytic oxidation is approximately 3 C/(cm²·μm), and the film production speed will be approximately 2 μm/min with electrical current having a planar current density of 100 mA/cm². At this time, if the planar current density is designated as D1 (mA/cm²), the electrolysis time is designated as T (min), and the necessary thickness of the AAO film is designated as H (μm), T=50·H/D1 (min). In addition, if the film production speed is designated as S, S=0.02·D1, and therefore T=H/S. If the length of the strip immersed in the electrolytic solution is designated as L (m) and the running speed of the strip is designated as LS (m/min), LS=L/T=0.02·L·D1/H=L·S/H. The running speed LS is proportionate to L and D1 or S, and inversely proportionate to H.

FIG. 9 is a graph that illustrates the relationship between running speed and AAO film production speed in the case that the thickness H of the AAO film is set to 10 μm. (a), (b), and (c) in FIG. 9 respectively denote cases in which the length L of the electrolysis tank is 5 m, 10 m, and 15 m. The running speed LS can be increased proportionate to the AAO film production speed S. In the case of the present invention, the length L of the electrolysis tank is a distance along the power supplying drum which is immersed within the electrolytic solution. For example, the electrolysis tank length can be set to 5 m if the diameter of the power supplying drum is 3 m and the drum is immersed slightly deeper than the center thereof. The AAO film is formed only on a single surface of the strip and the other surface remains metallic. Therefore, anodization can be continuously performed while supplying power through the drum. Accordingly, the running speed can be increased by a factor of N if N electrolysis tanks are arranged in series. (b) and (c) in the graph of FIG. 9 respectively illustrate running speeds in cases that two and three electrolysis tanks are arranged in series. Note that the vertical axis on the right side of the graph of FIG. 9 denotes electrolytic current that flows in the running direction of a strip per a width of lcm within a complete immersion type electrolysis apparatus to be described later. In the case of the present invention, this current does not flow as described previously, and power is directly supplied from the back surface of the strip.

As described previously, it is necessary to cause electrolytic current to flow from a power supply portion to an electrolysis tank in the running speed of a strip in a conventional electrolysis apparatus in which the strip is completely immersed. At this time, if the electrolytic current that flows in the running direction of a strip per a width of 1 cm is designated as D2 (A/cm), the amount of electrical current necessary to grow an MO of a necessary thickness on an area of a strip immersed in the electrolysis tank per unit time will be D2=LS·H·[coulombic efficiency]·100/60=5·LS·H. In this formula, the running speed LS is expressed as m/min, the thickness H of the AAO film is expressed as μm, and the coulombic efficiency is 3 C/(cm²·μm). Accordingly, D2 is an electrical current which is proportionate to the running speed and the thickness of the AAO film, and does not depend on the AAO film formation speed or the electrolysis tank length. The values indicated on the vertical axis on the right of the graph of FIG. 9 are for cases in which the thickness of the AAO film is 10 μm. Therefore, D2=50·LS with respect to the left vertical axis LS of the graph.

Meanwhile, there is an upper limit to the electrical current that can flow from the power supply portion of a strip to an electrolysis tank. In the case that the thickness of aluminum foil is 100 μm, the danger that meltdown will occur will increase by IR heat generation due to the resistance of the aluminum that results in thermal runaway if the electrical current exceeds 150 A/cm. Accordingly, it is necessary for the electrolysis current in the width direction to be 150 A/cm or less, that is, it is necessary for the running speed to be 3 m/min or less, regardless of the film formation speed or electrolysis tank length during electrolysis in the graph of FIG. 9. The IR heat generation limit electrical current and the meltdown limit electrical current of the strip are determined by the resistance per unit cross sectional area. Therefore, the limit electrical currents will become smaller as the aluminum foil is thinner. In addition, the limit electrical currents are also small for composite cladding materials, in which metals having high strength and high resistance such as steel, stainless steel, and Ti are combined with aluminum, and it is necessary for running speeds to be decreased for these materials as well.

Note that in principle, it is also possible to improve line speeds by installing a plurality of conventional electrolysis apparatuses, in which strips are completely immersed, in series as multiple steps. However, such a configuration is not realistic, because masking film adhering steps and masking film removing steps will also become necessary in the case that an AAO film is to be formed on only a single surface. In addition, in the case that indirect power supply is employed as a power supply method in the complete immersion type electrolysis apparatus, a power supplying tank is provided, and a voltage having a polarity opposite that of anodization is applied. Accordingly, if a plurality of electrolysis tanks are provided in multiple steps and indirect power supply is performed, a reverse voltage will be applied to an AAO film which is produced in an apparatus of a previous step during the power supply step, resulting in abnormalities such as separation of the AAO film. In the case that AAO films are to be formed on both surface of a strip, masking films are unnecessary. However, AAO coating films are insulative. Therefore, if AAO coating films are formed on both surfaces of the strip, multiple step power supply is not only impossible, twice the electrolytic electrical current that flows in the running direction is necessary compared to a case in which an AAO coating film is formed on a single surface according to the previously described calculations. Accordingly, it becomes even more difficult to increase running speed. For these reasons, continuous anodizing apparatus of the present invention is an extremely effective configuration for cases in which AAO films having thicknesses of 1 μm or greater are to be formed on a single surface of thin aluminum foil or a cladding material having high resistance. 

1. An anodizing apparatus, characterized by comprising: a power supplying drum for supporting a strip of an anodizable metal or a strip of a composite conductive metal foil having an anodizable metal on at least one surface thereof in close contact, at least a portion of the power supplying drum which is in close contact with the strip being constituted by a conductive material; opposing electrodes provided to face the power supplying drum; an electrolysis tank filled with an electrolytic solution in which a portion of the power supplying drum that supports the strip in close contact and the opposing electrodes are immersed; protective members formed by a non conductive material that overlaps the transverse ends of the strip supported by the power supplying drum in close contact and portions of the power supplying drum with which the strip is not in close contact to protect the ends and the portions of the power supplying drum from the electrolytic solution; and a drive section that causes the strip in close contact with the power supplying drum and the protective members to move together within the electrolytic solution, synchronized with the rotating speed of the power supply drum.
 2. An anodizing apparatus as defined in claim 1, characterized by: a recess that the strip contacts and moves within being provided in the power supplying drum.
 3. An anodizing apparatus as defined in claim 1, characterized by further comprising: guide rollers for pressing the protective member onto the power supplying drum.
 4. An anodizing apparatus as defined in claim 1, characterized by: a plurality of apertures being provided in the opposing electrodes.
 5. An anodizing apparatus as defined in claim 1, characterized by: the distance between the power supplying drum and the opposing electrodes at the portion of the strip supported by the power supplying drum that enters the electrolytic solution and/or the portion of the strip that exits the electrolytic solution being greater than the distance between the power supplying drum and the opposing electrodes at a central portion of the strip immersed in the electrolytic solution.
 6. An anodizing apparatus as defined in claim 1, characterized by: the protective member being non conductive rubber or a metal foil covered by nonconductive rubber.
 7. An anodizing apparatus as defined in claim 1, characterized by: the conductive material of the power supplying drum being conductive plastic or conductive rubber.
 8. An anodizing apparatus as defined in claim 1, characterized by: the electrical potential of the opposing electrodes being a negative polarity with respect to ground.
 9. An anodizing apparatus as defined in claim 1, characterized by: the electric potential of the strip being the same as ground, and the output of an electrolytic power source being insulative with respect to ground.
 10. An anodizing apparatus as defined in claim 8, characterized by: the electric potential of the strip being the same as ground, and the output of an electrolytic power source being insulative with respect to ground.
 11. An anodizing apparatus as defined in claim 10, characterized by further comprising: a monitoring section for monitoring the voltage of the power supplying drum with respect to the electrical potential of ground.
 12. A continuous anodizing apparatus, characterized by comprising: a plurality of anodizing apparatuses as defined in claims 1, arranged in series.
 13. A film forming method, characterized by: forming an anodized coating film on a surface of a strip, employing an anodizing apparatus as defined in claim 1 or the continuous anodizing apparatus of claim
 12. 